An accelerated mouse model of inflammatory dry eye disease

Meibomian glands (MGs) in eyelids (Fig. 1A) are enlarged sebaceous glands connected to hair follicles. The function of MGs is to secrete lipids which form the outer layer of the tear film of the eye (Fig. 1B). This layer maintains tear film stability by preventing tears from evaporating. Meibomian gland dysfunction (MGD) is a chronic abnormality of the Meibomian gland, commonly characterized by a change in the quantity or quality of the lipid secretion. MGD is among the most frequently diagnosed eye diseases and is a major cause of Dye Eye Disease (DED), but very little is known about the pathogenic processes leading to MGD and DED

Histopathology and selective biomarker expression in human meibomian glands

BACKGROUND/AIMS: Meibomian gland dysfunction (MGD) is the most common form of evaporative dry eye disease, but its pathogenesis is poorly understood. This study examined the histopathological features of meibomian gland (MG) tissue from cadaver donors to identify potential pathogenic processes that underlie MGD in humans. METHODS: Histological analyses was performed on the MGs in the tarsal plates dissected from four cadaver donors, two young and two old adults, including a 36-year-old female (36F) and three males aged 30, 63 and 64 years (30M, 63M and 64M). RESULTS: The MGs of 36F displayed normal anatomy and structure, whereas the MGs of 30M showed severe ductal obstruction with mild distortion. The obstruction was caused by increased cytokeratin levels in association with hyperproliferation, but not hyperkeratinisation. In two older males, moderate to severe MG atrophy was noted. Cell proliferation was significantly reduced in the MG acini of the two older donors as measured by Ki67 labelling index (6.0%±3.4% and 7.9%±2.8% in 63M and 64M, respectively) when compared with that of the two younger donors (23.2%±5.5% and 16.9%±4.8% in 30M and 36F, respectively) (p\u3c0.001). The expression patterns of meibocyte differentiation biomarkers were similar in the older and younger donors. CONCLUSION: Our histopathological study, based on a small sample size, suggests potentially distinct pathogenic mechanisms in MGD. In the young male adult, hyperproliferation and aberrant differentiation of the central ductal epithelia may lead to the obstruction by overproduced cytokeratins. In contrast, in older adults, decreased cell proliferation in acinar basal epithelia could be a contributing factor leading to MG glandular atrophy

Activation of Unfolded Protein Response in Transgenic Mouse Lenses

Transgene overexpression in mouse lens can activate unfolded protein response (UPR) in the lens fiber cells. Activation of UPR may contribute to defective and degenerative changes in the fiber cells. This study implies the levels of UPR activation should be assessed when using transgenic techniques to study gene function in vivo

Fibroblast Growth Factor Receptor 2 (FGFR2) Is Required for Corneal Epithelial Cell Proliferation and Differentiation during Embryonic Development

<div><p>Fibroblast growth factors (FGFs) play important roles in many aspects of embryonic development. During eye development, the lens and corneal epithelium are derived from the same surface ectodermal tissue. FGF receptor (FGFR)-signaling is essential for lens cell differentiation and survival, but its role in corneal development has not been fully investigated. In this study, we examined the corneal defects in F<i>gfr2</i> conditional knockout mice in which Cre expression is activated at lens induction stage by Pax6 P0 promoter. The cornea in <i>LeCre, Fgfr2^loxP/loxP</i> mice (referred as <i>Fgfr2^CKO</i>) was analyzed to assess changes in cell proliferation, differentiation and survival. We found that <i>Fgfr2^CKO</i> cornea was much thinner in epithelial and stromal layer when compared to <i>WT</i> cornea. At embryonic day 12.5–13.5 (E12.5–13.5) shortly after the lens vesicle detaches from the overlying surface ectoderm, cell proliferation (judged by labeling indices of Ki-67, BrdU and phospho-histone H3) was significantly reduced in corneal epithelium in <i>Fgfr2^CKO</i> mice. At later stage, cell differentiation markers for corneal epithelium and underlying stromal mesenchyme, keratin-12 and keratocan respectively, were not expressed in <i>Fgfr2^CKO</i> cornea. Furthermore, Pax6, a transcription factor essential for eye development, was not present in the <i>Fgfr2^CKO</i> mutant corneal epithelial at E16.5 but was expressed normally at E12.5, suggesting that FGFR2-signaling is required for maintaining Pax6 expression in this tissue. Interestingly, the role of FGFR2 in corneal epithelial development is independent of ERK1/2-signaling. In contrast to the lens, FGFR2 is not required for cell survival in cornea. This study demonstrates for the first time that FGFR2 plays an essential role in controlling cell proliferation and differentiation, and maintaining Pax6 levels in corneal epithelium via ERK-independent pathways during embryonic development.</p></div

Cre, Pax6 and keratocan immunofluorescence in corneas of <i>Fgfr2</i>^flox/+ heterozygous mice with and without <i>Le-Cre</i> transgene at P5.

<p>A, B) Cre was expressed in corneal (arrows) and conjunctival (small arrows) epithelium of <i>Le-Cre;Fgfr2</i>^{<i>flox/+</i>} eyes (B), but not in <i>Fgfr2</i>^{<i>flox/+</i>} eyes (A). C-F) Pax6 expression was found in corneal (arrows, D) and conjunctival (small arrows, D) epithelium, and keratocan expression in corneal stroma (E, F). The expression patterns of these proteins were similar in corneas between <i>Fgfr2</i>^{<i>flox/+</i>} (C, E) and <i>Le-Cre;Fgfr2</i>^{<i>flox/+</i>} eyes (D, F). Note that histological artifact caused the corneas in <i>Fgfr2</i>^{<i>flox/+</i>} eyes (without eyelids) to appear slightly thinner than those in <i>Le-Cre;Fgfr2</i>^{<i>flox/+</i>} eyes (with eyelids).</p

Corneal mesenchymal cell differentiation at E16.5 in <i>WT</i> and <i>Fgfr2</i>^CKO eyes.

<p>A, B) Keratocan expression was found in the stroma (S) of <i>WT</i> cornea, indicating the formation of keratocytes. Keratocan was not detected in the stroma of <i>Fgfr2</i>^<i>CKO</i> cornea, suggesting that normal differentiation of corneal mesenchymal cells into keratocytes was disrupted. C, D) N-cadherin was expressed in corneal endothelium (En, arrows) in both <i>WT</i> and <i>Fgfr</i>^<i>CKO</i> corneas. N-cadherin was also highly expressed in the lens epithelium (LE) in both genotypes. (AC = anterior chamber.)</p

Pax6 immunofluorescence.

<p>A, B) In E12.5 <i>WT</i> and <i>Fgfr2</i>^CKO eyes, Pax6 was expressed in developing corneal epithelial (CE), lens (L) and retinal (R) cells. The expression patterns were similar between <i>WT</i> and <i>Fgfr2</i>^<i>CKO</i> eyes. C, D) At E16.5, Pax6 expression was found in corneal and conjunctival epithelium in <i>WT</i> eyes (C) but was significantly reduced in corneal epithelium of <i>Fgfr2</i>^<i>CKO</i> eye, with a weak signal detected in a few cells (arrows in D). LE, lens epithelium. E, F) Deletion of <i>Mapk1</i> and <i>Mapk3</i>, encoding for ERK2 and ERK1 respectively, in the surface ectodermal-derived tissues severely affected lens and corneal development (H&E staining in E and E’). However, Pax6 expression appears to be normal in these tissues (F and F’).</p